The present invention relates generally to sub-sea oil and gas wells. More particularly, the present invention relates to a pump for reducing the density of a drilling fluid in sub-sea oil and gas wells.
When drilling sub-sea oil and gas wells, typically a hollow cylindrical tube (commonly referred to as a riser) is inserted into the ocean from the ocean surface to the ocean floor. A string of drill pipe as well as drilling fluid (commonly referred to as drilling mud, or mud) may be placed within the hollow portion of the cylindrical tube. This column of fluid is commonly referred to as the mud column. Generally, the density of the drilling mud is up to 50% greater than the density of the seawater.
At deep water levels, the pressure exerted by the drilling mud on the ocean floor is significantly greater than the pressure exerted by the seawater on the ocean floor. This higher drilling mud pressure can fracture the well bore extending below the ocean surface. If this happens, the drilling has to stop until the well is sealed, typically by use of casings. For deepwater wells, it is not unusual to run out of casing strings because each subsequent casing string has to be run inside the previous casing string.
Various methods have been produced to solve this problem, including installing pumps on the ocean floor to pump the drilling mud to the ocean surface, thereby reducing its apparent pressure. Another method involves decreasing the drilling mud density by injecting lighter materials into the mud column thereby creating a mixture that has a lighter density than the drilling mud. Buoyant spheres have been advantageously used for this method because they can be easily manufactured from high strength, low density materials that can withstand high pressures while also decreasing the drilling mud density.
In order to be effective, the spheres need to be pumped down to the a lower end of the mud column, near the drilling surface on the ocean floor, and injected into the mud column. However, conventional pumps cannot supply the amount of force necessary to pump relatively large spheres to the ocean floor. As a result, small spheres must be used. However, small spheres are not as efficient at decreasing the drilling mud density as large spheres are. In addition, once the spheres return to the upper end of the mud column, they must be separated from the drilling mud, so that both the drilling mud and the spheres may be reused. It is much easier to separate large spheres from the drilling mud than it is to separate small spheres from the drilling mud.
An exemplary embodiment of the present invention includes a pumping system for injecting buoyant spheres into an oil or gas well comprising: a feeder containing a plurality of buoyant spheres; and a sphere pump in proximity to the feeder, having first and second rotatable wheels, wherein the first wheel has a plurality of notches and the second wheel has a corresponding plurality of notches, such that during rotation of the wheels the first and second wheel notches temporarily combine to form a plurality of pockets, wherein each pocket receives then ejects one of the plurality of buoyant spheres from the feeder during rotation of the first and second wheels.
In another embodiment of the present invention, the pumping system for injecting buoyant spheres into an oil or gas well further comprises a conveyance pipe having proximal and distal ends, wherein its proximal end is connected to an outlet of the sphere pump and its distal end is connected to a lower end of an oil or gas well; and a second pump in fluid communication with the conveyance pipe.
A further embodiment of the present invention includes a pumping system for injecting buoyant spheres into an oil or gas well comprises a feeder containing a plurality of buoyant spheres; a positive displacement sphere pump in proximity to the feeder, having first and second counter rotating wheels, wherein the first wheel has a plurality of generally hemispherical notches and the second wheel has a corresponding plurality of generally hemispherical notches, such that during rotation of the wheels, the first and second wheel notches temporarily combine to form a plurality of generally spherical pockets, wherein each pocket receives then ejects one of the plurality of buoyant spheres from the feeder during rotation of the first and second wheels; a conveyance pipe having proximal and distal ends, wherein its proximal end is connected to an outlet of the sphere pump and its distal end is connected to a lower end of an oil or gas well; and a second pump in fluid communication with the conveyance pipe.
Another embodiment of the present invention includes a method of reducing a density of a drilling fluid in an oil or gas well comprising: conveying a plurality of buoyant spheres to a feeder; providing a sphere pump in proximity to the feeder, which applies a first force to the plurality of buoyant spheres, wherein the sphere pump is connected to a proximal end of a conveyance pipe and wherein a distal end of the conveyance pipe is connected to a lower end of a portion of an oil or gas well that is adjacent to the drilling fluid; providing a second pump in fluid communication with the proximal end of the conveyance pipe, which applies a second force to the plurality of buoyant spheres, wherein the first and second forces cause the buoyant spheres to be injected into the drilling fluid to decrease the density of the drilling fluid.